This invention relates generally to the field of so-called in-line capping machines adapted to seat and tighten successive caps exiting from a cap chute upon serially advancing containers having an upwardly facing neck forming an opening, and more particularly to an improved quill assembly incorporating a novel clutch construction which permits the transmission of torque upon an engaged cap to be maintained within prescribed limits. Devices of this general type are known in the art, and the invention lies in specific constructional details which permit improved operation and ready manual adjustability required when the capping machine is used for installing a variety of caps upon a corresponding variety of containers. Reference is made to U.S. Pat. Nos. 3,214,887, dated Nov. 2, 1965; and 3,435,587 dated Apr. 1, 1969, both patents being granted to Arthur W. Weller, and assigned to the same assignee as the instant application, these patents disclosing the environs of the present invention. Cap applying machines of the disclosed type are characterized in including an endless conveyor belt which advances in serial fashion a plurality of open containers beneath a plurality of rotatively driven quill elements, half of which are disposed on either side of the contaners at a height wherein a driven frictional wheel or disc will engage the cylindrical surfaces of an applied screw or bayonet type cap delivered to a point of engagement with a container, and rotated to tightened condition to thereby seal the contents of the container.
In the past, the degree of applied torque was not particularly critical. Most caps were fabricated from metal, and were not easily damaged. An excessively tightly fitted cap was manually removed with difficulty, but usually without damage either to it or the engaged container.
In more recent years, there has been a much greater use of screw-type caps formed from synthetic resinous materials, particularly in the area of "child-proof" caps which are formed to include an inner and an outer element normally turn free of each other in the absence of manually applied pressure along the axis of the cap, tending to bring the inner and outer elements into mutually engaged condition. The outer element is often a thin plastic shell which is easily cracked during the capping operation. This condition will escape notice at the time, and will in many cases prevent proper functioning of the cap at the time of subsequent manual removal. Where the crack is a peripheral one having an axis parallel to the axis of the cap, the sharp edges defining the crack form a safety hazard to the fingers of the user as well. While the application torque may be reduced under such conditions, too little torque, particularly where the contents of the containers are in liquid form, gives rise to the possibilities of leakage of the same before use.
The problem has been recognized in the prior art, and crude attempts at solution have been made. The most simple expedient is to clamp the driven friction disc at the bottom of the quill element under an adjustable pressure, such that the disc will slip under excessive applied torque. The shortcoming of this structure lies in the fact that effectively, one of the clutch "plates" is of highly resilient material, and static friction under load is too loosely related to the clamping pressure applied against the disc. Further, with continued slippage, the wear on the planar surface of the disc effectively changes the clamping pressure, whereby frequent adjustment is necessary to maintain a reasonably constant maximum available torque.